Which system has infinitely many solutions?
{2x−y=54x−2y=9\begin{cases} 2x - y = 5 \\ 4x - 2y = 9 \end{cases}{2x−y=54x−2y=9
{x+2y=42x+4y=8\begin{cases} x + 2y = 4 \\ 2x + 4y = 8 \end{cases}{x+2y=42x+4y=8
{3x+y=23x+y=5\begin{cases} 3x + y = 2 \\ 3x + y = 5 \end{cases}{3x+y=23x+y=5
{x−y=12x−2y=3\begin{cases} x - y = 1 \\ 2x - 2y = 3 \end{cases}{x−y=12x−2y=3